Presently, there exists apparatus for wrapping a load, such as a number of layers of boxes that are stacked and supported on a pallet. The load is wrapped in film or tape to provide protection from the ingress of moisture to the load in the case of a film wrapping, and to provide support for and to secure the stacked boxes in situations where both film or tape is used. The load typically rotates on a turntable as tape or film is unravelled from a roll such that the tape or film wraps sequentially each side of the layers of boxes. The roll is supported on a mast for vertical movement to enable film or tape to be applied to the load in a predetermined pattern and to cater for varying heights of the load. There exists a need for a specific automated process to wrap a load such that the vertical movement of the roll of film or tape and the rotation of the turntable is controlled according to a control program, for example a computer program. Such an automated process is more efficient in that it saves time, uses less film or tape in that the load is rapped or secured in a predefined pattern.
There is also a need to provide a means for controlling the rate at which tape is applied to the load depending on which portion of the load is being wrapped. There is also a need to provide a requisite amount of tension in the tape as it is applied to the load so that as the load is rotating there is substantially no slack or too much tension in the actual tape being applied to the load.
Furthermore, the present invention provides a pre-tensioning apparatus for tensioning a stretchable material, such as tape, prior to the tape being applied to a load to be wrapped. The tape is required to be stretched or pre-tensioned to a length representing a multiple of its unstretched length so that when the tape is wrapped around the load it will partially shrink or reduce in length so as to wrap tightly and securely around a load. This process also reduces the length and volume of tape required. By using the present invention, loads to be wrapped may be done so by choosing a particular pattern of wrapping that secures the load with minimum usage of tape material. This has the benefit in reducing the amount of wasted tape or film material and thereby reduces costs associated with disposal of the unused or wasted material.
Present systems rely on a gearing mechanism whereby one gear is brought into engagement with another gear, having a different number of teeth, to pre-stretch the tape. A problem with such systems is that when the teeth of the different gears engage, they are wedged in tightly against each other. Consequently, the gears can bind and therefore require more force to feed the tape between rollers connected to the meshed gears providing the requisite tension to the tape. In some instances, the greater force required breaks the tape which is an obvious disadvantage. The present invention provides a unique way of pre-stretching the tape that eliminates binding of the meshed gearing arrangement and a facility for feeding tape through the assembly either under tension or not under tension for reasons that will become apparent from further reading of this specification.
Another problem identified in prior art systems in applying adhesive tape in a stretched condition to a load is that when the tape initially has to be placed on the load in an unstretched condition, the tape adhered to the surface of rollers of a pre-stretching apparatus which stopped a suer guiding the tape through the rollers in order to adhere the tape to a side of the load. This was due to the rollers being made from rubber compounds which provided too much friction for unstretched adhesive tape resulting in a build-up of deposited adhesive. With the tape caught or stuck on the rollers, the tape was difficult to peel off the rollers and eventually this led to the rubber compounds of the rollers wearing out. The rollers subsequently had to be replaced often. Aluminium rollers have been used but proved ineffective. The present invention seeks to address these problems by providing rollers in a pre-tensioning apparatus that enables tape to traverse through the rollers in both stretched and unstretched conditions.